For reasons I can’t explain, it sometimes seems like historic moments pile up around certain weeks of the year. We mourn in late January for too many astronauts lost. New Years’ and the Fourth of July celebrate the great landings and flybys of so many missions. And this weekend, inexplicably, brings us two anniversaries in planetary exploration. 

On Monday, we celebrate the 1974 flyby of Mercury made by Mariner 10. If you try Googling this mission, you will learn the Mercury car line had its own Mariner edition, and I really hope this is a call back to this great little spacecraft that left the Earth before I was born. 

Mariner 10 was the last of its line of spacecraft. This series of missions made the first flybys of all the worlds in the inner solar system, entered orbit around another planet for the first time, and sent us back the crushing news that Venus is too hot for life and Mars is a desert world without canals or seas. Science fiction was forever changed by these missions, and the modern era of planetary science was started. From Mariner 10, NASA moved on to developing the Voyager and Viking programs, and the technology of these missions eventually evolved into the Cassini mission.

When Mariner 10 reached Mercury, cameras took what for 33 years would be our only closeup images of Mercury. Growing up, these images, mosaiced together with poorly matched backgrounds, filled my textbooks, and remarkably, they would go on to reveal new science thanks to modern image processing software like Photoshop. In the years leading up to MESSENGER’s arrival at Mercury, these images were reprocessed and revealed amazing details thanks to modern methods, showing that sometimes technology can reveal more than we imagined even in data we already have.

Tomorrow is the fiftieth anniversary of the start of Viking experiments to look for life on Mars. To be clear, those actual experiments occurred in 1976, but their origins go back to a 1971 lab experiment to see if conditions simulating those on Mars could produce organic compounds, and those experiments showed they could. Those results led to the inclusion of three different experiments on the Viking landers that looked to stimulate interactions with microbes in various ways; experiments that were inconclusive, with one researcher, Gilbert Levin, saying life had been found, and that in an analysis of images even lichens could be seen on surrounding rocks.

These results continue to be controversial. The result that seemed to indicate there was life is one in which they provided nutrients to the soil and looked to see if that soil outgassed materials that incorporated that stuff it had been fed. And if it did, here on Earth, that is a sign of life in the soil. And we saw this on Mars, but because the other experiments that were run did not also find life, it has been easier to simply say either life was not found or the results were inconclusive, leaving poor Levin to a lifetime of screaming to the wind, “Yes, there is life on Mars!” and a constant appeal to replicate these experiments – a replication that still hasn’t been done.

Today, the Perseverance rover is out there, not looking for these kinds of active signals and being able to interact with today’s life. It’s instead looking for fossils. But I hope someday soon, someday before Levin – who ran the experiment in 1976 – passes away, we will have further understanding of just what happened with his experiments that all started in a lab fifty years ago tomorrow.

More Information

50 years ago, experiments hinted at the possibility of life on Mars (ScienceNews)

40 years ago, Viking 1 pioneered U.S. exploration on Mars (ScienceNews)

Mariner 10 info page (NASA)

Viking 1 Lander info page (NASA)

I’m Convinced We Found Evidence of Life on Mars in the 1970s (Scientific American)